This invention relates to controlled release formulations and, in particular, to sustained release powders consisting of discrete micro-particles.
Many types of controlled or sustained release pellets are known which are loaded into capsules for oral administration. These pellets can be described as macro-particles and invariably have an average size greater than 400 .mu.m.
Sustained release pellets cannot be readily formulated as liquids. Sustained release liquids are desirable for use as geriatric and pediatric formulations.
Various processes are known for the production of micro-spheres using solvent evaporation emulsion techniques. Known micro-encapsulation technique are generally employed for phase transformation, such as for the conversion of liquids to solids. Alternatively, such techniques may be used for protecting an active material, such as coating aspirin to mask its stomach irritant properties.
Sustained release liquids are known which contain ion exchange resins. In such sustained release liquids the active ingredient is bound to an ion exchange resin in the form of a reversible complex and is displaced therefrom in vivo. Such sustained release liquids are described, for example, in French Patent Publication No. 2 278 325.